Got it to work!
I had the same problem. My new Samsung Note 8 would not connect to my 1 yr old JVC Bluetooth car stereo.
I updated the firmware on my JVC Bluetooth car stereo, no luck.
I updated the the Note 8 and cleared the Bluetooth cache, no luck.
Ultimately, I noticed I had about five devices registered to my JVC stereo, mostly my old phones, tablets and devices. I removed all of these connected devices from my JVC stereo and Bam!, I then retried to add my new Note 8 and it connected immediately.
Apparently, my JVC stereo had a limit of number devices.
Hope this helps someone.
Jon